Examples of material suitable for recycling are paper with pulp content, paperboards, cartons, fiberboards, packing material or bio waste. Such recycled material may contain various impurities that may not be utilized in the same process with the recycled material, such as plastic, sand, glass, metal and blocks of wood. These impurities must be removed from the recycled material, for example from pulp, before the pulp is used in further processes. Purified pulp may be utilized in making paper or carton, while purified bio waste is suitable for producing biogas. The impurities may be utilized in other processes.
FI118970 discloses one method for cleaning impurities from recycled paper, wherein separate pulpers and processing stages of the rejected recycled material have been connected with pipework or screw conveyors. Hereinafter in this document the rejected recycled material is referred to as reject and the accepted recycled material is referred to as accept. The description according to FI118970 of the method for purifying recycled material comprising paper and paperboard is hereby incorporated by reference. In one embodiment, between vertical pulpers there is one vertical clarifying pipe for separating heavier rejects. The rejects from the first pulper travel to the last pulper through the clarifying pipe to be slushed and purified. From the last pulper, coarse reject is transferred with a slanted screw conveyor to reject processing—in this example a two-part rotating reject drum. Gravitation moves the reject from the first pulper to the last pulper. Tall vertical pulpers require a high reaching and long conveyor for the first pulper, thus requiring plenty of space of the processing facility. If the process must be interrupted, due to malfunction or due to sequential processing, removing the coarse material is very time-consuming. The duration of the material removal process is equal to the material purifying process. Long duration of the material removal process decreases the overall capacity.